1. Field of the Invention
The present invention relates to a tunable matching network which may be coupled to a microwave transmission line.
2. Brief Description of the Related Art
As indicated in a presentation by F. Durodie on New Antenna Impedance Evaluation and Matching Tools for TEXTORS's ICRH System, at the 16th Symposium on Fusion Technology (SOFT), London, Sep. 3-7, 1990, a tunable matching network, is required, for example, for a microwave transmission line which couples high power microwave energy into the plasma combustion chamber of a fusion reactor. Since the plasma combustion chamber represents a constantly changing load resistance to the microwave transmission line and in order for the generator generating the microwave energy not to be damaged by reflections which are the result of a mismatch, each occurring load resistance must be transformed to the characteristic impedance of the line. According to the mentioned publication, two tunable capacitors which are separated from one another by the length of a transformation line, which must be measured precisely, are coupled to the microwave transmission line for this purpose. Tuning of the capacitors is the result of a mechanically elaborate pneumatic device. However, since the load resistance may change very rapidly, this arrangement would be too slow to bring about matching that is as free of delay as possible.
A tunable matching network may not only be used in the case described, but at any time a changing resistance impedance is switched on to a microwave transmission line.